1. Field of the Invention
This invention relates in general to magnetic transducers and in particular to a gapped magnetic head of the type in which the length of its gap is selectively alterable.
2. Description Relative to the Prior Art
There are many instances when it would be desirable to alter dynamically the effective length of the gap of a magnetic head. In the recording, for example, of video information on magnetic tape having high coercivity, it would be desirable to record the video information by means of a head having a fairly long record gap, thereby to maximize the level of recording flux. By contrast, it would be desirable to play back the recorded video information by use of a head having a playback gap that is extremely short, thereby to reproduce video signals of extremely short wavelength. The provision of a magnetic head having a "versatile gap" is, however, not new. U.S. Pat. No. 3,686,467, for example, discloses a variety of teachings for dynamically altering the effective length of a magnetic head gap. In certain embodiments of U.S. Pat. No. 3,686,467, the gap is formed of a layer of field-saturable magnetic material and a layer of non-magnetic material. By applying a saturating flux to the saturable material, the effective gap is lengthened; without the application of the saturating flux, however, the gap has an effective length that is equivalent to the thickness of the non-magnetic layer. Various techniques are indicated for saturating the saturable material. In another embodiment of U.S. Pat. No. 3,686,467, the gap is formed of a layer of non-magnetic material and a layer of magnetic material of low Curie temperature. By selectively heating the gap material, the gap assumes a length corresponding to the combined thickness of the non-magnetic and low-Curie-temperature materials; without the application of heat to the low-Curie-temperature material, however, the gap has a length corresponding to the thickness of the non-magnetic material. Other gap-altering techniques, stemming from the above-described general embodiments of U.S. Pat. No. 3,686,467, are also described in U.S. Pat. No. 3,686,467.
U.S. Pat. No. 4,346,417 in the name of Neil J. Griffith and assigned to the assignee hereof concerns the dynamic formation, and closure, of (a) gap(s) of precise dimensions. The disclosure of U.S. patent application Ser. No. 133,076 indicates a multitrack head having saturable material occupying completely the respective gap regions of the cores of the head. By magnetically saturating the gap material of one head core, that head core is turned ON; head cores which do not receive gap-saturating flux are, however, left in their respective OFF states. Since any head core which is OFF is, magnetically, of a toroidal form, inductive coupling between those cores which are OFF and the core which is ON cannot, inherently, cause the recording of ghost information by means of the OFF cores, i.e. induced flux is trapped within the "toroidal" OFF cores.
The invention, as will appear below, is practicable with either of the above-described concepts: the length of a core gap may be lengthened/shortened from one discrete size to another; or a core may be provided, or not, with an effective gap of a given discrete size.